Military meal (4)
I believe the answer is:
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">military meal</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for mess that I've seen before include "dish" , "Communal dining room" , "Confused person" , "Meal" , "Eating place" .)